1. Field of the Invention
The present invention relates to a fluid separator, a hollow fiber to be used for construction thereof and a process for the preparation of this hollow fiber. More particularly, the present invention relates to a hollow fiber type fluid separator comprising hollow fibers having fins on the periphery thereof, such a hollow fiber, and a process for the preparation thereof.
As the fluid separation intended in the present invention, there can be mentioned liquid separation such as dialysis, ultrafiltration, precision filtration, pervaporation, or reverse osmosis and gas separation such as oxygen enriching in air.
2. Description of the Related Art
Fluid separators comprising hollow fibers having a selective permeability have been practically used for the reverse osmosis or hemodialysis.
Especially, hollow fiber type blood dialyzers have been vigorously used for purifying blood of patients suffering from the renal insufficiency. In a blood dialyzer of this type, many permeable membranes, for example, hollow fiber membranes, are filled in a shell, and blood of a patient is passed through the hollow interiors and a dialyzing solution (or dialysate) is passed outside the membranes, that is, spaces among the membranes. Wastes in the blood are removed through the hollow fibers by dialysis to correct the electrolyte concentration, and by producing a difference of the pressure between the inside and outside of the hollow fibers, excessive water is removed from the blood by ultrafiltration. Furthermore, hollow fibers are used for remedy of an autoimmune disease by separating only plasma from blood or removing a specific component from the separated plasma. Hollow fibers to be used for such blood treatments should allow selective permeation of specific solutes according to the intended use. The capacity of a hollow fiber depends on the material, the porosity (pore size and pore number) and the membrane thickness of the hollow fiber. For example, it is important how a number of hollow fibers should be bundled so as to increase the dialyzing efficiency of the entire membrane surface. For example, when hollow fibers are arranged in the longitudinal direction closely to one another, the dialyzing solution does not flow uniformly around the hollow fibers but forms specific flow paths, with the result that dialysis is hardly performed through hollow fibers not participating in these flow paths and the entire dialyzing effect is reduced. In the ordinary dialytic operation, the difference of the concentration between the inside and outside of the hollow fiber membrane is a driving force for the transport of the solute. Accordingly, it is necessary to make a contrivance on the shape of the hollow fiber per se so that the dialyzing solution flows through the outside space of the hollow fiber as uniformly as possible, the area having a larger boundary layer resistance is reduced as much as possible and the difference of the concentration between the blood side (the inner side of the hollow fiber) and the dialyzing solution side (the outer side of the hollow fiber) is increased.
As means for solving this problem, there has been proposed a method in which by increasing the amount contained (filling ratio) of hollow fibers in a dialyzer shell to some extent, a certain flow resistance is given to a dialyzing solution to uniformalize the flow thereof. Furthermore, there has been proposed a method in which hollow fibers are crimped or cover yarns are wound around the hollow fibers to prevent contact of the hollow fibers with one another and increase the efficiency of the transport of the solute by the flowing of the dialyzing solution. However, these methods are still insufficient and further improvements are desired.